Spark ignition engines may be prone to combustion knock under high loads. Following spark ignition, areas of the uncombusted air/fuel mixture may self-ignite, causing a large pressure wave that resonates the engine block. Increased air charge temperatures, increased compression ratios, and lower fuel octane levels may exacerbate the problem. A typical method for mitigating engine knock includes retarding the spark ignition timing, thus slowing the combustion burn rate. However, this also has the effect of decreasing fuel economy and deteriorating engine performance during wide open throttle conditions.
Similarly, boosted engines may be prone to cylinder pre-ignition when operating at high load and relatively low engine speed. Cylinder pre-ignition may manifest as “mega-knock”, producing high-pressure spikes that may damage engine components. Cylinder pre-ignition is typically addressed by reducing engine load. However, this also reduces engine performance.
Gasoline engines utilizing late injection timing may be particularly prone to combustion knock and cylinder pre-ignition. Late injection of gasoline may cause deposits of soot and/or particulate matter within the cylinder. This in turn may free oil that may act as an ignition source for combustion knock or cylinder pre-ignition.
The inventors herein have realized that the above issues may be addressed in part by one or more methods. In one example, a method for an engine, comprising: during a first condition comprising a high engine temperature, injecting a first quantity of liquid petroleum gas into a first engine cylinder at a first timing during an intake stroke; and injecting a second quantity of liquid petroleum gas into the first engine cylinder at a second timing during a compression stroke following the intake stroke. In this way, combustion knock and cylinder pre-ignition may be mitigated without retarding spark ignition and/or limiting engine load, thereby allowing for maximum engine performance.
In another example, a method of mitigating combustion knock in a liquid-petroleum gas fueled engine, comprising: in response to the detection of combustion knock in a first engine cylinder, port fuel injecting a first quantity of fuel into the first engine cylinder when an intake valve of the first cylinder is open; direct fuel injecting a second quantity of fuel into the first engine cylinder when the intake valve of the first cylinder is closed; port fuel injecting a third quantity of fuel into a second engine cylinder when an intake valve of the second cylinder is open; and direct fuel injecting a fourth quantity of fuel into the second engine cylinder when the intake valve of the second cylinder is closed. In this way, combustion knock may be mitigated without retarding spark ignition from minimum best timing, or by reducing the amount of spark ignition retard from minimum best timing, thereby allowing for maximum fuel economy and maximum engine performance during wide open throttle conditions.
In yet another example, a method of mitigating cylinder pre-ignition in a liquid-petroleum fueled engine, comprising: in response to the detection of cylinder pre-ignition in a first engine cylinder, port fuel injecting a first quantity of fuel into the first engine cylinder when an intake valve of the first cylinder is open; direct fuel injecting a second quantity of fuel into the first engine cylinder when the intake valve of the first cylinder is closed; port fuel injecting a third quantity of fuel into a second engine cylinder when an intake valve of the second cylinder is open; and direct fuel injecting a fourth quantity of fuel into the second engine cylinder when the intake valve of the second cylinder is closed. In this way, cylinder pre-ignition may be mitigated without limiting engine load, or by reducing the amount of engine load limiting, thereby allowing for maximum engine performance.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.